A pneumatic tire has historically been sought which has a reliable means of retarding or stopping its deflation upon being punctured. Such a tire would reduce the frequency of tire changes on our high-speed interstate highways, thereby resulting in increased safety for the motoring public. Because attention to vehicle safety is on the increase, many vehicle and tire manufacturers have become interested in equipping vehicles with pneumatic tires having the capability of either sealing or reducing the rate of inflation loss after puncture. Some vehicle and tire manufacturers have become interested in equipping vehicles with such a tire in conjunction with a low-pressure warning device that would inform the motorist when the tire-inflation pressure drops below a prescribed amount and then the "slow-leak" feature of such a tire would allow the motorist to take corrective action.
Various approaches to achieve a sealant or "slow-leak" pneumatic tire have been proposed without lasting commercial success. One approach that has been proposed is to attach a layer of elastomer sealant containing no curatives to the inside of the unvulcanized tire. The tire is then vulcanized resulting in an unvulcanized sticky layer of elastomer on the inside of the vulcanized tire which acts as a sealant. This approach has not had significant commercial success because of manufacturing, technical, and economic problems associated with producing such a tire. The unvulcanized layer of elastomer sealant has a tendency to stick to the curing bladder thus causing high amounts of unacceptable tires.
The above problems are overcome by applying the sealant to a vulcanized tire. U.S. Pat. No. 3,935,893 discloses a sealant which can be applied to a vulcanized tire. In U.S. Pat. No. 3,935,893, the sealant is made up of a combination of high-molecular weight curable butyl rubber, a liquid polybutylene tackifier, a partially hydrogenated block copolymer of styrene and a conjugated diene, carbon black and suitable curing agents for the butyl rubber components.
New tire-sealant compounds which can be added to vulcanized tires or built into unvulcanized tires are desirable.